1. Field of the Invention
This invention relates to a process and apparatus for determining the X, Y and Z positions in a three dimensional scene at close range.
2. Background Information
The need to measure positions on a three-dimensional ("3-D") surface has long existed. In fact, the entire industry of cartography and photogrammetry has developed as a result of this long felt need.
Recently, various devices have been developed to measure 3-D surfaces at close range. Such applications have been for engineering or product line inspection purposes. For example, U.S. Pat. No. 4,653,316 to Fukuhara describes an "Apparatus Mounted On Vehicles For Detecting Road Surface Conditions." This device comprises a laser beam for illuminating a road surface for the purpose of determining the location of cracks in the road. This system, however, employs separate distance detecting means in order to determine the distance from the sensor to the illuminated area on the road and does not rely on photogrammetric technologies of data reduction. It is fundamentally a two dimensional imaging system and does not render a 3-D image of the road surface.
U.S. Pat. No. 4,842,411 to Wood describes a "Method Of Automatically Measuring The Shape of a Continuous Surface." This invention is drawn to the task inspection of manufactured parts. The system is not designed to be portable nor to create the continuous map of X, Y and Z positions which might be necessary in other applications. Further it comprises a full X-Y array of charge-coupled devices which adds to the system cost.
In addition the type of light used to illuminate the object being inspected is not constant over the object thereby possessing error which must be compensated for.
U.S. Pat. No. 4,937,445 to Leong et. al is designed to determine the distance between a reference axis and points on an object. This invention is designed to determine thicknesses of materials in a manufacturing environment. However, it does use laser illumination techniques to avoid light source problems. It is not designed to be a portable system nor to address the wide variety of photogrammetrically significant 3-D scenes that exist. The illumination technique used cause the laser beam to be split into many segments instead of relying upon a single beam illumination. Further this device only measures distances from a reference axis and does not create a full X, Y, and Z datapoint record of a scene.
U.S. Pat. No. 4,534,650 to Clerget et. al describes a "Device for Determination of the Position of Points on the Surface of a Body." This patent does describe a laser beam successively illuminating pinpoint regions on the surface of a body. Two views of a 3-D scene are taken. The images are also recorded on discrete linear photosensitive elements. This invention, however, requires that the sensor be moved relative to the object being imaged or vice versa in order to obtain 3-D surface data, an obvious disadvantage for field operations.
In addition to these above factors, none of these inventions is designed to be combined with other data sources or superimposed on other image data from the same scene.
It is therefore an objective of the present invention to develop a system which is both portable and very easy to use in a wide variety of photogrammetrically significant situations at close range situations requiring precise measurement of 3-D surfaces using photogrammetric methods. Further, it is an objective to create an inexpensive photogrammetric laser system that relies solely upon one-dimensional photosensitive arrays which are readily available together with a unique optical system that allows the determination of X, Y positions within an image plane using solely a single photosensitive array and the X and Y direction by moving a laser for illumination rather than relocating the system or the scene.
It is a further an objective of the present invention to create a photogrammetric laser system that can accurately detect and locate the X, Y and Z positions of an object using photogrammetric methods and use such information together with a visual image collected during the measurement.
It is another objective of the present invention to create a system whereby the X, Y and Z measurements derived can be correlated with a conventional video image of the scene.
It is a further objective of the invention to create a photogrammetric laser system that is easily calibrated through collection of data over a known surface.
Finally, it is a key objective of the Photogrammetric Laser System to accurately measure an entire scene in a very brief (less than a minute) period of time without any human intervention.